If an expected date has been set in your accounting platform this will be imported across to Float and used to show where the invoice falls in the cash flow. You can update this expected date in Float, however if a different expected date is added in your accounting platform this will overwrite the changes made in Float.
Similarly if an invoice doesn't have an expected date one can be added in Float. If an expected date is then added in the accounting platform this will overwrite the date added in Float.
On the flip side, changing expected dates in Float does not change the expected date in the accounting platform.